Frictional-retarding means

ABSTRACT

Improved frictional-retarding means containing at least one cast iron brake surface. The improvement consists in constructing said brake surface of a cast iron consisting essentially (i) of from 2 percent up to 5 percent by weight of phosphorus, (ii) silicon, and (iii) carbon, with the total of said silicon and carbon being less than 6 percent, and (iv) the remainder being essentially iron. Minor amounts of the impurities usually found in cast iron may be tolerated.

United States Patent Inventors Eric Douglas Henley Derby;

George Eden Walker, Solihull, both of England June 26, 1968 Nov. 16, 1971 Albright & Wilson Limited Warwickshire, England; British Railways Board London, England July 7, 1967 Great Britain Appl. No. Filed Patented Assignees Priority FRICTIONAL-RETARDING MEANS 9 Claims, No Drawings US. Cl 188/251 M, 75/123 CB, 75/123 D, 75/132, l88/73.2, 188/218 R, 192/107 M Int. Cl Fl6d 69/02 Field of Search 188/251 M,

73.2,218; 192/107 M; 75/123 CI, 123 P, 132

[56] References Cited UNITED STATES PATENTS 1,690,352 6/1927 Williams 75/123 3,533,758 10/1970 Lowe et al. 29/180 1,527,165 2/1925 Bennett 75/123 C1 2,402,424 6/1946 McCauley 75/123 D 3,193,383 7/1965 Butler 75/123 C1 3,318,423 5/1967 Dunki 188/251 FOREIGN PATENTS 463,311 3/1937 Great Britain 75/123 Cl Primary Examiner-George E. A. Halvosa Attorneyl-lerbert H. Goodman ABSTRACT: Improved frictional-retarding means containing at least one cast iron brake surface. The improvement consists in constructing said brake surface of a cast iron consisting essentially (i) of from 2 percent up to 5 percent by weight of phosphorus, (ii) silicon, and (iii) carbon, with the total of said silicon and carbon being less than 6 percent, and (iv) the remainder being essentially iron. Minor amounts of the impurities usually found in cast iron may be tolerated.

FRICTIONAL-RETARDING MEANS The present invention relates to iron/phosphorus alloys which exhibit a high degree of wear resistance and are therefore of value in articles wherein iron castings are subjected to frictional wear, e.g., frictional-retarding means, and especially frictional-retarding means employed in an environment which may present a fire hazard.

When a cast iron material is brought into frictional contact with a surface moveable in relation thereto there is a tendency for fine particles of iron to be removed from the mass. The particles may be heated by the friction to a temperature at which exothermic reaction occurs with the air. A consequence of this tendency for fine particles of iron to be removed from the mass. The particles may be heated by the friction to a temperature at which exothermic reaction occurs with the air. A consequence of this tendency is that brake shoes and similar iron-containing masses which are subjected to high frictional forces experience rapid wear and tend to omit persistent hot sparks. Where such frictionally heated iron masses are employed in an environment where the hot sparks can come into contact with flammable material, such as for example with fuel oil on diesel locomotives, or in mining machinery a serious fire hazard results.

We have now discovered that, when at least 2 percent by weight of phosphorus is incorporated in an iron-containing mass and the resulting ferrous alloy is exposed to frictional forces, then notwithstanding the production of some metallic dust, the wear on the alloy compared with that on ordinary cast iron is substantially reduced, and moreover, the emission of sparks is very considerably reduced. Moreover, the physical properties of the ferrous alloy are such that the alloy is particularly suitable as a replacement for cast iron parts used in friction brake systems, for example in the manufacture of brake shoes, drums or discs.

Our invention therefore provides, in articles of the type wherein iron castings are exposed to frictional wear, the improvement of constructing the castings of an iron containing at least 2 percent of phosphorus by weight of the total iron and phosphorus. Preferably, the proportion of phosphorus is 2.4-5 percent.

Our invention further provides frictional-retarding means comprising an iron-containing mass having incorporated therein at least 2 percent by weight of phosphorus based on the total weight of iron and phosphorus and means for bringing the said mass into frictional contact with a surface which is moveable in relation thereto.

Preferably, our invention provides a brake system comprising a first rotatable brake surface, and a second brake surface adapted to be brought into frictional contact with the first brake surface so as to retard the rotary motion of the latter, wherein at least one of the brake surfaces comprises iron and from 2-5 percent of phosphorus.

According to a further aspect, our invention provides a brakeshoe comprising a block of an alloy consisting of cast iron having incorporated therein from 2 to 5 percent by weight of phosphorus, and provided with means for attachment to a brake system as aforesaid.

According to a further aspect our invention provides rotary brake members, such as drums or discs, adapted for use in a brake system as aforesaid and constructed of cast iron having incorporated therein from 2-5 percent by weight of phosphorus.

The invention is also applicable to brake systems wherein the first brake surface is a reciprocating member, or a member such as a rail which is in continuous linear motion relative to the second surface.

The brake surface or other casting is preferably constructed from an alloy consisting of 85 to 95 percent by weight iron, 2 to 5 percent by weight phosphorus, less than 6 percent total weight of carbon and silicon and less than 5 percent total weight of other metals. Generally, the other metals, such as manganese, cobalt, nickel, vanadium, chromium, tungsten and molybdenum, are present in a total proportion of less than 1 percent and preferably less than 0.75 percent. Typically the alloy has a composition corresponding to conventional grey cast iron, except for the high phosphorus content.

Preferably, the phosphorus is added to cast iron in the form of ferrophosphorus which is available as a byproduct from the production of phosphorus in an electrothermal furnace, and may also be produced by reduction of phosphatic ore in the presence of iron. Ferrophosphorus so obtained is an alloy of iron and phosphorus which usually contains from 23 to 27 percent by weight of phosphorus.

Thus, ferrophosphorus may be incorporated into cast iron in the proportions necessary to provide an alloy with the desired .phosphorus content. The incorporation may conveniently be carried out in a cupola in which initially alternate charges of coke and a mixture of iron and ferrophosphorus or other phosphorus-supplying component) are laid down. The whole is heated by the burning of the coke in a blast of air and the process is then usually caused to operate continuously by the introduction of the top of the cupola of a mixed charge of iron, ferrophosphorus and coke while the molten iron-containing product is run off from the base of the cupola. The molten mass is conveniently poured from a ladle into a series of moulds to provide castings capable of being used in the frictional-retarding means of the invention, for instance as brake shoes, drums or discs. The iron charge to the cupola need not consist of pig iron, but may conveniently consist of, or include a proportion of broken-up iron castings and/or scrap steel. As an alternative, the alloys for use in our invention may be prepared directly by reduction of phosphatic iron ore in a blast furnace.

In some circumstances, it may be desirable in the manufacture of the present frictional retarding means to employ a sintered metal or to find a granular phosphorusand iron-containing mass with a suitable resinous or ceramic material.

Any conventional means may be used for attaching a brakeshoe of our invention to a brake system, which may be actuated by mechanical, pneumatic or hydraulic means.

As articles of the invention having a braking surface made of the aforesaid alloy may be, for example, a brakedrum or disc. In use, this will be brought into contact with a second brake member which may for example, be a brakeshoe or disc or wheel and may also be made of the said alloy or of other material suitable for the purpose.

Brakeshoes in accordance with our invention are very suitable for use on railway vehicles, particularly on diesel locomotives, where their use near fuel oil, in places of cast iron brakeshoes, reduces the risk of fire as the result of sparks igniting the fuel oil, and in mining machinery where the danger of igniting coal dust or flammable gases is reduced. The present invention may also find use in a variety of other frictional retarding means, for example, in brake systems of the disc type, and such systems may be employed not only in all kinds of railway rolling stock and similar transport applications, but also in braking industrial machinery, marine engines, lifts and cranes.

The invention is also generally applicable to a wide range of articles of manufacture wherein iron castings are normally exposed to wear by frictional forces.

The invention is illustrated by the following examples.

EXAMPLES 1-2 A mixed charge of pig iron and ferrophosphorus of 24 percent phosphorus content was melted together and the resulting phosphorus containing alloy prepared in the from of castings. The mixed charge was of such proportions that different alloys were prepared as follows:

APPROXIMATE PHOSPHORUS CONTENT OF FERROUS ALLOY- Example 1 4 percent by weight Example 2 2 percent by weight The resulting castings were qualitatively assessed for use in frictional-retarding means by placing them in contact with a revolving grinding wheel. It was clearly apparent that the spark emission from each of the alloys was much reduced compared with conventional cast iron. Moreover, though each of the alloys suffered a little wear, this was small. Qualitative assessment of the castings suggested that the degree of reduction of spark emission increased with increase of phosphorus content.

EXAMPLE 3 A mixed charge of 2,063 pounds of scrap cast iron brakeshoes and 177 pounds of ferrophosphorus (phosphorus content about 25 percent) was placed in a cupola together with coke. The coke was burnt in an airblast and the resulting alloy was run off from the bottom of the cupola and used to cast a number of brakeshoes which an analysis were shown to contain 2.4 percent phosphorus.

The brakeshoes were shown to have a tensile strength between 11.25 and 12.30 tons per square inch, a transverse strength of 18.8-22.6 tons per square inch, a compression strength of 57.6-58.0 tons per square inch and a Brinell hardness (as tested on a bar of length 1.2 inches according to 8.8.8. 1452:1961) of 207-255. These properties compare favorably with the physical properties of conventional cast iron brakeshoes.

The spark emission properties of the brakeshoes were tested by placing them against a revolving grinding wheel and taking photographs of the sparks emitted. The sparks were shown to be considerably fewer, and their tracks shorter in length, than with conventional cast iron brakeshoes.

EXAMPLE 4 Examples 1-2 were repeated but with a charge of 1,965 pounds cast iron and 275 pounds ferrophosphorus. The resulting brakeshoes had a phosphorus content of 3.2 percent and exhibited a further reduction in spark emission compared with the brakeshoes of example 3, as evidenced by the same test, and with the additional evidence provided by placing slabs of foamed polystyrene at a set distance from the revolving grinding wheel and noting the degree of pitting which occurred on the surface thereof due to local melting of the polystyrene by the fine pyrophoric iron particles present in the sparks. The physical properties of the brakeshoes again compared favorably with those of conventional cast iron brakeshoes bemg:

Tensile strength 9.5l0.0 tons per square inch Transverse strength 16.4-19.6 tons per square inch Compression strength 52.8-55.2 tons per square inch Brinell hardness 212-255 EXAMPLE 5 Brake blocks were prepared as in example 3 containing (a) 3.75 and (b) 4.0 percent of phosphorus. The static and dynamic coefficients of friction of the blocks were measured and compared with those of a conventional cast iron brakeshoe. The results are tabulated below from which it is seen that there is generally a small increase in the coefficients from those for the conventional brakeshoe. This is advantageous since it means the braking efficiency is slightly improved, but that the increase is not so great that the increased frictional braking force would be liable to cause damage to the remainder of the braking system.

The tests on damaged steel surfaces were conducted on metal surfaces that had been roughened by severe metal to metal contact.

EXAMPLE 6 A total of 2,000 brake blocks containing 3 percent by weight of phosphorus were tested on 1,250 11.1. (type 2) diesel locomotives operating on severe gradients in the Inverness district over periods ranging from 3 to 12 months. Not only were fires prevented, despite the occurrence of incidents which would have been expected to cause fires using conventional brake blocks but the average life of brake blocks was found, surprisingly, to be substantially greater than that of conventional grade 12 cast iron brake blocks. Conventional brake blocks on this section of railway must be replaced after 21-25 days corresponding to 5,000-6,000 miles travelled. Brake blocks of our invention has an average life of 60 clays, corresponding to 12,000-l6,000 miles travelled. The braking characteristics were substantially the same as for ordinary cast iron brake blocks.

Thus, frictional-retarding means of our invention have an important advantage over ordinary cast iron, even in situations where no fire risk exists.

In the course of the above experiments it was noted that the flow properties of the molten iron/phosphorus alloys render them particularly suitable for casting, and show a marked improvement over conventional cast iron.

We claim:

1. In a frictional-retarding means comprising a first rotatable brake surface, and a second brake surface adapted to be brought into frictional contact with said first surface, the improvement which consists of constructing one of said brake surfaces of a cast iron consisting essentially of (i) phosphorus in an amount from 2 percent up to 5 percent by weight, (ii) sil icon and (iii) carbon, with the total of said silicon and carbon being less than 6 percent, and (iv) the remainder essentially iron.

2. The frictional-retarding means of claim 1 wherein said one brake surface is a brake drum.

3. The frictional retarding means of claim 1 wherein said one break surface is a brake disc.

4. The frictional-retarding means of claim 1 wherein said one brake surface is a railroad brake shoe.

5. The frictional-retarding means of claim 4 wherein the proportion of phosphorus is from 2.4-5 percent by weight.

6. The frictional-retarding means of claim 5 containing 2.4 percent phosphorus.

7. The frictional-retarding means of claim 5 containing 3 percent phosphorus.

8. The frictional-retarding means of claim 5 containing 3.2 percent phosphorus.

9. The frictional-retarding means of claim 5 containing 4 percent phosphorus. 

2. The frictional-retarding means of claim 1 wherein said one brake surface is a brake drum.
 3. The frictional retarding means of claim 1 wherein said one break surface is a brake disc.
 4. The frictional-retarding means of claim 1 wherein said one brake surface is a railroad brake shoe.
 5. The frictional-retarding means of claim 4 wherein the proportion of phosphorus is from 2.4- 5 percent by weight.
 6. The frictional-retarding means of claim 5 containing 2.4 percent phosphorus.
 7. The frictional-retarding means of claim 5 containing 3 percent phosphorus.
 8. The frictional-retarding means of claim 5 containing 3.2 percent phosphorus.
 9. The frictional-retarding means of claim 5 containing 4 percent phosphorus. 